1. Field of the Invention
The present invention relates to a silicon-containing copolymer, and more particularly to a photosensitive resin composition containing the silicon-containing copolymer. The silicon-containing copolymer is suitable for use as a top layer resist in a bilayer resist system.
2. Description of the Prior Art
With increasing integration of semiconductor devices, there is a heightened need to form finer patterns in photolithography processes. Both 248 nm and 193 nm photolithography technologies are necessitated in fabricating microelectronic devices, and many efforts have been made to develop a suitable photoresist material for operating at such short wavelengths.
When a single layer resist is used in short wavelength photolithography, even if an anti-reflection resist layer is applied, the depth of focus (DOF) will be decreased, and the stability control capacity of the process also decreases. Therefore, a bilayer resist has been developed to improve the resolution and the stability control capacity of the process. The bilayer resist includes a thicker underlayer of resin, which can planarize the substrate and decrease reflection, and a thinner silicon-containing top layer of a silicon-containing polymer, which is photosensitive and has good resistance to oxygen plasma etching.
Most of the silicon-containing polymer resists used in 193 nm bilayer resist are acrylate-based resins. The disadvantages follow. The acrylate-based resin is labile on the backbone. When the silicon content increases, the Tg of the resin decreases accordingly. In addition, since the acrylate-based resin is lacking in functional groups with high polarity, it has poor adhesion to the resin underlayer. Once a polar group is introduced into the acrylate-based resin, swelling occurs, which results in poor resolution. In addition, the acrylate-based resin has poor erosion resistance.
Therefore, in recent years, many researchers have attempted to develop new silicon-containing polymers for use as the top layer resist in the bilayer resist system. Boardman et al. [SPIE 3678, 562(1999)], Sooriyakumaran et al. [SPIE 3999, 128(2000)] and Kim et al. [SPIE 3999, 115(2000)] have all synthesized silicon-containing copolymers of maleic anhydride and norbornene. Since maleic anhydride and norbornene have more rigid structures than acrylate, the Tg of the resin is increased. In addition, the high polarity of maleic anhydride can enhance the adhesion between the resist top layer and the resin underlayer.
However, there is still a need to develop a novel silicon-containing copolymer suitable for a bilayer resist system, in order to further enhance the Tg of the resist resin system and the adhesion.
Therefore, an object of the present invention is to solve the above-mentioned problems and to provide a novel silicon-containing copolymer having a high glass transition temperature and a better polarity.
Another object of the present invention is to provide a novel silicon-containing copolymer having good adhesion to a resin underlayer for use in a bilayer resist system.
To achieve the above objects, the silicon-containing copolymer of the present invention includes a repeating unit represented by formula (I), a repeating unit represented by formula (VI), a repeating unit represented by a formula selected from the group consisting of formulae (II), (III), (IV), (V), and mixtures thereof: 
wherein
R7 is selected from the group consisting of hydrogen, C1-20 linear and branched alkyl, (C1-6alkoxy) (C1-10alkyl), (C3-20cycloalkyl) (C0-6alkyl), (C3-20polycycloalkyl) (C0-6alkyl), and (C3-10heterocyclic group) (C0-6alkyl),
R1, R2, and R3 can be the same or different and are independently selected from the group consisting of hydrogen, C1-20 linear and branched alkyl, (C1-6alkoxy) (C1-10alkyl), (C3-20cycloalkyl) (C0-6alkyl), (C3-20polycycloalkyl) (C0-6alkyl), (C3-10heterocyclic group) (C0-6alkyl), and a silicon-containing group, wherein the silicon-containing group is C3-50 silyl or (C3-50silyl) (C1-9alkyl), and the silyl can be substituted with an alkoxy substituent, and wherein at least one of R1 and R2 is the silicon-containing group,
R4, R5, and R6 can be the same or different and are independently the silicon-containing group, and
the moles of formula (I), the moles of formula (VI), and the sum of the moles of formulae (II), (III), (IV), and (V) are in a ratio of 1:0.05-0.8:0.2-0.95.
The silicon-containing copolymer of the present invention can be prepared from the corresponding repeating units by any suitable conventional polymerization method, such as, free radical, controlled radical or group transfer polymerization.
As mentioned above, the silicon-containing copolymer of the present invention includes at least three repeating units. The maleic anhydride repeating unit of formula (I) and the norbornene repeating unit of formula (VI) are necessary components for the silicon-containing copolymer of the present invention. Another component is at least one of the norbornene repeating units, having a silicon-containing group, represented by formulae (II), (III), (IV), and (V).
Formula (VI) is a repeating unit containing no silicon. Formulae (II), (III), (IV), and (V) are repeating units containing silicon.
The silicon-containing group indicated in the present invention is C3-50 silyl or (C3-50 silyl) (C1-9alkyl), wherein the silyl can be substituted with an alkoxy substituent. According to the present invention, at least one of R1 and R2 in formula (II) is the silicon-containing group, R3 in formula (III) can be the silicon-containing group, R4 is the silicon-containing group, and R5 in formula (IV) and R6 in formula (V) are the silicon-containing groups.
For example, the silicon-containing group can be selected from the group consisting of 
wherein
X, Y, and Z can be the same or different and are independently selected from the group consisting of C1-4 linear and branched alkyl, and C1-6alkoxy,
m, n, and p are 0 or integers of from 1 to 6.
A preferred example of the silicon-containing group is when X, Y, and Z are the same and are methyl or methoxy.
Representative examples of the silicon-containing groups include 
A representative example of formula (VI) is 
bicyclo[2.2.1]heptane-2-carboxylic acid tert-butyl ester (TBNB).
A representative example of formula (II) is 
5norbornene-2,3-dicarboxylic acid tert-butyl ester (trimethylsilyl) methyl ester (TMSTBNB).
A representative example of formula (III) is 
trimethylsilanyl-bicyclo[2.2.1]heptane-2-carboxylic acid 2-trimethylsilanyl-ethyl ester (DITSNB).
A representative example of formula (IV) is 
2-trimethylsilyl-5-norbornene (TSNB).
A representative example of formula (V) is 
bicyclo[2.2.1]heptane-2-carboxylic acid 2-trimethylsilanyl-ethyl ester (TSENB).
According to the present invention, R1, R2, R3, and R6 can be the same or different and can be acid-labile protective groups, which decompose in the presence of an acid, so as to make the silicon-containing copolymer alkali-soluble.
When R1, R2, R3, and R are acid-labile protective groups, the acid-labile protective group can be selected from the group consisting of: 
R7 can also be an acid-labile protective group, which decomposes in the presence of an acid, so as to make the silicon-containing copolymer alkali-soluble. When R7 is the acid-labile protective group, the acid-labile protective group can be selected from the group consisting of: 
The silicon-containing copolymer of the present invention can be soluble in an organic solvent, and has a weight average molecular weight (Mw) of 1000 to 5000 and a glass transition temperature (Tg) of 70xc2x0 C. to 150xc2x0 C. In addition, the silicon-containing copolymer of the present invention can be used as a top layer resist in a bilayer resist system.
The present invention also provides a photosensitive resin composition, which comprises:
(a) a silicon-containing copolymer including a repeating unit represented by formula (I), a repeating unit represented by formula (VI), a repeating unit represented by a formula selected from the group consisting of formulae (II), (III), (IV), (V), and mixtures thereof: 
wherein
R7 is selected from the group consisting of hydrogen, C1-20 linear and branched alkyl, (C1-6alkoxy) (C1-10alkyl), (C3-20cycloalkyl) (C0-6alkyl), (C3-20polycycloalkyl) (C0-6alkyl), and (C3-10heterocyclic group) (C0-6alkyl),
R1, R2, and R3 can be the same or different and are independently selected from the group consisting of hydrogen, C1-20 linear and branched alkyl, (C1-6alkoxy) (C1-10alkyl), (C3-20cycloalkyl) (C0-6alkyl), (C3-20polycycloalkyl) (C0-6alkyl), (C3-10heterocyclic group) (C0-6alkyl), and a silicon-containing group, wherein the silicon-containing group is C3-50 silyl or (C3-50silyl) (C1-9alkyl), and the silyl can be substituted with an alkoxy substituent, and wherein at least one of R1 and R2 is the silicon-containing group,
R4, R5, and R6 can be the same or different and are independently the silicon-containing group, and the moles of formula (I), the moles of formula (VI), and the sum of the moles of formulae (II), (III), (IV), and (V) are in a ratio of 1:0.05-0.8:0.2-0.95;
(b) 0.03-10 wt % of a photoacid generator; and
(c) 5-20 wt % of a solvent, based on the weight of the silicon-containing copolymer.
Any suitable photoacid generator may be used. Preferred photoacid generators include, but are not limited to, triarylsulfonium salts, diaryliodonium salts, sulfonates, and mixtures thereof. Representative examples of the triarylsulfonium salts include triphenylsulfonium triflate, triphenylsulfonium antimonate, tris-4-methoxyphenyl-sulfonium triflate, tris-4-methoxyphenylsulfonium antimonate, tris-4-methylphenylsulfonium triflate, and 1-naphthyl methyl-substituted alkylsulfonium triflate. Representative examples of the diaryliodonium salts include diphenyliodonium triflate, di-t-butylphenyliodonium antimonate, and di-t-butylphenyliodonium antimonate.
Suitable solvents can be ethers, ethylene diol ethers, aromatic hydrocarbons, ketones, esters, or mixtures thereof.
The photosensitive resist composition of the present invention can further include (d) a killer base in an amount of 1-20 mole % based on the mole of (c) photoacid generator. The killer base can be an amine or an ammonium salt, for example, a trialkyl amine or a tetraalkyl substituted ammonium salt.
The photosensitive resist composition of the present invention can be photosensitive at a wavelength of UV, deep UV, vacuum UV (300 nm-100 nm), extreme UV (11 nm-13 nm), electron-beam, or X-ray, preferably at a wavelength of 193 nm or 153 nm.
The photosensitive resin composition of the present invention can be used as a top layer in a bilayer resist system. First, a resin underlayer is coated on a silicon wafer and then cured by baking. Next, the photosensitive resin composition of the present invention, which includes the silicon-containing copolymer, is coated on the silicon wafer with the resin underlayer and then baked to form a top layer.
The wafer, which has been coated with the resin underlayer and the silicon-containing top resist layer, is exposed to radiation through a mask and then baked. Upon exposure, the acid-labile group in the silicon-containing copolymer of the present invention is removed. Thus, the exposed region of the top layer can be removed by developing the wafer with a conventional developer. Thus, a pattern of the top layer can be formed.
The patterned wafer is then subjected to oxygen plasma etching. In the unexposed region, silicon contained in the surface of the top layer will react with oxygen plasma to form nonvolatile products (i.e., SiO2). In the exposed region, the underlayer will react with oxygen plasma to form volatile products and will be readily evaporated by etching. Therefore, the pattern of the silicon-containing resist top layer can be transferred to the resin underlayer accordingly.
With regard to the resin underlayer, the resin suitable for use in the present invention can be phenolic resins, particularly novolak resins, such as formaldehyde cresol or formaldehyde phenol novolaks, polyimide resins, poly(meth)acrylate resins and styrene-allyl alcohol copolymer resins.
The present invention provides a novel silicon-containing copolymer having a high glass transition temperature and a better polarity. The silicon-containing copolymer of the present invention can be used in a bilayer resist system and has good adhesion to a resin underlayer.
The following examples are intended to illustrate the process and the advantages of the present invention more fully without limiting its scope, since numerous modifications and variations will be apparent to those skilled in the art.
Preparation of Silicon-containing Copolymer